1. Field of the Invention
The present invention relates to an ISDN (integrated services digital network) terminal adapter for coupling non-ISDN terminal equipment to the ISDN network.
2. Description of the Related Art
The ISDN terminal adapter is a device that is used to provide protocol conversions between non-ISDN terminal equipment such as X.25 data terminal equipment and the ISDN. Transmission of a 128 kbps signal from such terminal equipment is carried out by using the B1 and B2 channels of the basic rate of the ISDN interface. The transmitted signal is divided into 64-kbps component signals at the entry point of the network and transmitted over separate paths to an exit point of the network where they are byte-interleaved into a 128-kbps data stream and forwarded to the destination terminal equipment. Since the separate paths are established independently in the network, there is a difference in path length between the transmitted signals, so that they arrive at the destination at different times.
In order to compensate for the path length difference, the 128-kbps signal received at the destination terminal is byte-deinterleaved into component signals and respectively stored into two buffer memories each with a capacity sufficient to hold the respective component signal. If the unit of data to be transmitted is 500 kilobytes, each buffer memory is required to store 250 kilobytes of data. Therefore, it is desired to reduce the amount of memory for timing difference compensation.